120' Mooney & Weaver, GSA Memoir 72, 1989

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1 120' Mooney & Weaver, GSA Memoir 72, 1989

2 120' Mooney & Weaver, GSA Memoir 72, 1989 Frasetto et al., Geosphere, 2011 Big incompatibility here. What is the deal?

3 120' Mooney & Weaver, GSA Memoir 72, 1989 Frasetto et al., Geosphere, 2011

4 6.6s 4.5s no lag ~3 s ~2 s no lag Byerly, BSSA, 1937 Times are delays from expected arrival time. No lag from EQs near Eureka to Fresno. Also no lag in Pg.

5 n ' i ESE er EQs on west of Sierra: Arrival late I. 4OO Distance (km) Savage et al., Tectonics, 1994 Arrivals at station just east of the Sierra late for events from west--this section shows what that looks like.

6 n ' i ESE Byerly 1938 er EQs on west of Sierra: Arrival late I. 4OO Distance (km) Savage et al., Tectonics, 1994 That was the seismic observations was there support elsewhere?

7 P L A T E A U A R E A O C E A N A R E A 9 8 0, r O o Q o S? ' 9 7 9, _ ISOSTATIC RESIDUAL i uu i -100 r Simpson & Jachens, GSA Memoir 72, 1989 First we need to have a basic idea of how gravity anomalies work.

P L A T E A U A R E A O C E A N A R E A 9 8 0, 0 0 0 r O o Q o S?

8 P L A T E A U A R E A O C E A N A R E A 9 8 0, r O o Q o S? ' 9 7 9, _ ISOSTATIC RESIDUAL i uu i -100 r in essence, we find that gravity anomalies are smaller (more negative) the higher you go, indicating isostasy is active.

9 0, -75 ' _... _ -,oo r erveo _z Computed ' -,, -175 '.... Computed Effect of.... Crustal Root... o _ 200 Gravity Profile across Sierra ' '"'"' - A' -150 o - ;)50 - Z75 -Z75 5 )olton Boss Loke LEVEL ' ;.;.I;.;.;.;.;,. '.'.. i:; i'i :'. S,erro Gloss Crest29 Long Volley Mounto,n 5 SEA LEVEL 5 ]0 15 zo i:i:i:i:i:::::::::::::::::: :::::::::: ::::: :: :: ::::: ::i:i:i:i:i:i:i:i:i:i:i i:i i:i:!:i:i:i:i:!:::: ::::::::::::: :::::::::::::i:i::::::::::::: Z5 z o!"-'- ' -.j "' ' '-' ;J il "' ' ' '" ' } ' '"' ' ' ' :;. ii:.'.. ii :.:':i ;i ' -'-; '",;";';;'i' ;;'.'.a;¾ : :i:i:!: :i:i:!:i:... : : :i:!:i:!:!... 4O... ;.....'..'...'! _'.;". {i '... w' ' ' " ' '.;.- ' : "- ' -'-'.. '..,_'.,, - '.'-,:.. """ c ' '.. '" ' '' ' "''' ' '...'._ ':.<:. 5o ' ' ' "' '"' - v' '..-. ;t ' j'. a '- ' '',', ; lt '''... ''"',. - 45! :: :: :: i :: i :: i :: i :: i i :: ::?:::i::::ii::!::i ::::::::::::::::::::::::::::::::::::::::::::: ::::::::::::il i::::::i::::::!: :. '.'.:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: _, : ;' '"' :' ':. "' ::. ::... :... " '- 5O 35 Cenozo,c sed mentory and volcanic rocks Cretaceous and Upper Juross c gronlhc rocks of the S,erro Nevodo bothohth Pre-Cretoceous metamorphic rocks Unknown rocks m the lower IX t of the earth's crust Unknown rocks,n the upper part of the eorth's montle 0 S lto 15 i 20 f 25 f S?. 75 l Oliver et al., GSA Bull, 1961 but there are multiple ways of interpreting this.

10 Eaton, CDMG Bull 190, 1966

11 Eaton, CDMG Bull 190, 1966

12 Time, t slope = sin(i up-dip intercept= t2d = 2zd cos(ic)/v1 c -α)/v 1 = 1/v 2u slope = 1/v 2d +i c)/v 1 = sin(α down-dip intercept= t2u = 2zu cos(ic)/v1 slope = 1/v1 distance x zd hd ic ic ic = sin-1 (v1/v2) α zu hu Eaton, CDMG Bull 190, 1966

13 If we approximate crust as 6.55 km/s, then: From intercepts: Moho at Mono Lake end 60 km bsl Moho at China Lake end 50 km bsl Dip of 2.0 From apparent velocities: Dip to north of 2.2 Velocity of 7.9 km/s Eaton, CDMG Bull 190, 1966 Note that Pn only a first arrival from north at very south end of profile

14 120' Mooney & Weaver, GSA Memoir 72, 1989

$Refraction line$ Sierra, 1993,

15 Refraction line across the southern Sierra, 1993, clearly eliminated a thick root.

16 37 Bouguer Gravity (mgal)

17 d = Airy Root ρc h (ρm - ρc) Pratt Crustal Root ρ = ρc h (hc + h) Pratt Mantle Root ρc h ρ = hm Crust ρc h ρc ρ h hc ρc h ρm d ρ hm Mantle Constant Pn velocity Large dips on Moho Constant Pn velocity No dips on Moho Variations in surface geology? Varying Pn velocity No dips on Moho No variations in surface geology Jones et al., JGR, 1994

18 East-West Profile through the Sierra Nevada Comparing Different Compensation Styles Airy Root ρc h d = (ρm - ρc) Pratt Crustal Root ρc h ρ = (hc + h) 50 Isostatic anomaly Crust ρc h ρc ρ h hc 0 ρm Mantle d mgal Bouguer anomaly Constant Pn velocity Large dips on Moho Constant Pn velocity No dips on Moho Variations in surface geology? Pratt Mantle Root ρc ρc h ρ = hm h Airy Root Pratt Crustal Root Pratt Mantle Root km ρ hm Varying Pn velocity No dips on Moho No variations in surface geology Jones et al., JGR, 1994 Note the large isostatic anomaly (blue line) for an Airy root but much smaller anomaly if using lateral variations in the crust

19 East-West Profile through the Sierra Nevada Comparing Different Compensation Styles 50 Isostatic anomaly 0 Comparison of density variations across the Sierra at 36.5 N mgal -100 Bouguer anomaly observed surface densities (Sikora et al., 1991) Airy Root Pratt Crustal Root Pratt Mantle Root density variation in top 30km to support Sierra density km Pratt Crustal Root ρc h ρ = (hc + h) ρc ρ h hc km E of ' Jones, unpublished Constant Pn velocity No dips on Moho Variations in surface geology? Jones et al., JGR, 1994 Red line is a smoothed fit to observed densities.

20 5O 120 ø 119 ø 118 Gravity - density. o b ':'.1.. N Slope = 6.8 km Δg =2πGρt ' Dmsity (g/cm 3) slope = 2πGt 3.0 ' /ri.:.:.:...:.:.:,:.:.: :.:.:...i.:.:...:.: Grid cell locations 37 ø 36 ø, ',' ' Elevation - gravity 3- Elevation- density e" ee e.- e e o -50 e el e e lee... ) i Isostatic residual gravity (regal) Dex ity (g/cm 3) 3.0 Saltus & Lachenbruch, Tectonics, 1991 rhoc is x, delta g is y, so slope is

21 Isostatic anomaly vs. density, southern and central Sierra Isostatic gravity anomaly (mgal) ; D = 2.0 ± 0.6 km ; D = 6.9 ± 0.32 km y = m1*m0 + m2 Value Error m m Chisq NA R NA y = m1*m0 + m2 Value Error m m Chisq NA R NA density (g/cc)

22 Bouguer anomaly vs. density, central and southern Sierra 0 Bouguer gravity anomaly (mgal) ; D = 8.0 ± 1.6 km ; D = 22.6 ± 1.2 km density (g/cc)

23 -250 Southern Sierra: Individual Gravity Measurements Bedrock Localities -200 complete Bouguer anomaly (mgal) Station elevation (m)

24 Sierra Nevada heat flow vs. heat production Explanation Data source Distance from Basin and Range >40 <40 km usos A A other I l--l this study O 100 q 0 = DA + q r CNB... " 'HMN O... K_NDY,-. TAHO RKY... JAC.-'''' O THW... H_C ' ' RVN... BL LK.. -'... A... DOME_.''... THE at'... Sierra Nevada linearelation'... D = 10 km, qr - 17 mw/m Heat production ( W/m 3) Saltus & Lachenbruch, Tectonics, 1991

25 Saltus & Lachenbruch, Tectonics, 1991

27 House et al., Nature, 1998

28 Jones et al., Geosphere, 2004 We know there is a big variation in heat production (left)--what is the impact on shallow geotherms

29 Jones et al., Geosphere, 2004

30 Jones et al., Geosphere, 2004

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